Laserfiche WebLink
Rifle Gravel Pit#1 Project No.21-010R-C2 <br /> Garfield County,Colorado <br /> 3.0 SLOPE STABILITY ANALYSES— PROPOSED CONDITIONS <br /> Slope stability modeling was conducted to evaluate the factor of safety with respect to slope <br /> geometry and subsurface conditions. We were provided with development plans for the Rifle <br /> Gravel Pit#1 prepared by SGM and dated 9/1/2022. Based on our review of the plans, we <br /> believe the final reclamation grading would be the more conservative evaluation. The addition <br /> of the berm to the top of the slope will increase driving forces, which would not be present <br /> during mining operations, and reduce the global factor of safety for the slope. <br /> We selected two locations along the south side of the project to conduct slope stability <br /> evaluations. The section locations are presented on Figure A-1 attached. The section <br /> geometry and water surface elevation were based on proposed grading from Sheet 5 of the <br /> SGM plans. The stability was modeled using limit equilibrium (LE) method of slices using the <br /> shear strength methodology. <br /> The LE method uses the slope profile to divide the model into vertical sections with each section <br /> contributing to the driving and resisting forces. The forces are summed, and a factor of safety is <br /> calculated as the ratio of the sum of resisting forces to the sum of driving forces. A factor of <br /> safety (FS) of 1.0 can be interpreted as the resisting forces equal the driving forces and the <br /> overall slope is at equilibrium. A less than 1.0 indicates the resisting forces are less than driving <br /> forces, or a slope below the limit of equilibrium (the slope is failing). A FS greater than 1.0, for <br /> example a FS of 1.30, indicates the total resisting forces are 30% higher than total driving <br /> forces. A FS of at least 1.30 is typically a target design value for most slopes. <br /> 3.1 STABILITY MODEL <br /> Figure 1 depicts the slope stability model for the west section. The section profile was <br /> estimated from the plans prepared by SGM. The model suggests a FS of 2.0 which is well <br /> above the minimum typical standard of 1.3. In addition, the theoretical failure surface is at least <br /> 40 feet from the nearest existing utility line. <br /> 2 <br />